There has been considerable interest in isolating bioactive compounds from marine organisms. Typical procedures involve in vitro screening programs to test crude extracts for antimicrobial, antiviral, and cytotoxic activities. Illustrative examples of known bioactive compounds from marine sources include bryostatins, ecteinascidins and furthermore didemnins where didemnin B, also now known as aplidine, is the first marine natural product in clinical testing.